Hi Syed,
As per details provided by you I think PR lock means no changes allows in Purchase requisition, but SAP gives feasibility that you can make changes in PR in the quantity, valuation price & Purchasing Group if the purchase order is created for the that particular Purchase requisition.
Same applies with RFQ.
Please let us know if PR locks means something else as per your requirement.
thanks & regards,
Ankur Chauhan